Over the past decade, a class of flexible line cutting devices for trimming grass and other vegetation around trees, fences and the like, or edging along sidewalks and the like, has achieved widespread acceptance in the marketplace. These devices usually contain a supply of monofilament nylon line stored on a spool with a free end extending from an aperture in a head rotating at typically between 3,000-8,000 r.p.m. A number of systems have been devised to maintain a cutting swath having a diameter of from 12 to 20 inches for various motors of different power is typical. So long as the spool and housing rotate at the same speed, no additional line is payed out. However, when the spool is allowed to rotate relative to the housing, or the housing to rotate relative to the spool, an additional length of line is payed out to replenish the line as it is lost due to wear or breakage.
The so-called bump-feed system is the most widely used to control the payout of line to maintain the desired cutting length. In one type of device typified by U.S. Pat. Nos. 4,183,138 and 4,274,201, for example, the housing is driven by the drive shaft of the prime mover and the storage spool is disposed to reciprocate along the axis of rotation relative to the housing, first upwardly in response to tapping a member connected to the spool against the ground, and then downwardly in response to a spring biasing the spool back to the normal running position. An escapement mechanism limits the maximum relative rotation between the housing and the spool to thereby limit the amount of line payed out. When urged to the upward position by engagement with the ground the spool is released from a first set of locking teeth and allowed to rotate a short increment as a result of the centrifugal force pulling on the line which s being rotated in the cutting plane before engaging a second set of escapement teeth which prevents further rotation. Upon being returned by the spring to the lower position, the spool is allowed to rotate an additional predetermined increment before again being restrained by the lower set of escapement teeth, thus paying out a controlled increment of line. The operator may repeat this procedure as often as required while operating the device.
In another similar device, such as disclosed in U.S. Pat. No. 4,189,833, the spool is driven by the prime mover and the housing is reciprocated axially relative to the spool to achieve indexing and line payout.
In yet a third distinct class of bump feed devices is represented by the device disclosed in U.S. Pat. No. 4,236,309, where neither the spool nor housing is axially reciprocated, but a third member is reciprocated to achieve payout. These devices are significantly more complex and expensive to fabricate, assemble, and to replace an exhausted supply of line.
In the first described system, drive power is coupled from the shaft to the housing, then through the escapement teeth to the spool and associated ground bumping mechanism. In the second system, power is applied from the shaft to the spool, then through the tooth mechanism to the housing. In each system, the spring must be disposed between the housing and the spool, tending to urge one downwards from the other. When the supply of cutting line on the spool is exhausted, the device must be disassembled by removing either the spool from the driven housing or the housing from the driven spool. In either case, the spring disposed between the two must also be removed. Line is then either rewound on the spool, or a new spool with line is used. The line is first threaded through the aperture in the housing, then the housing and spool urged into position by compressing the spring. The difficulty of threading the line from the spool through the aperture while inserting the spool into the housing against the force of the spring is a difficult and substantial and inconvenience for many customers. Further, for effective manufacturing costs, it is desirable for a head to be usable when driven in either direction of rotation, with the line wound on the spool in either direction.
The present invention is concerned with an improved head assembly for dispensing a monofilament line in response to the operator bumping the head against the ground which has an arrangement of components that is cost effective to fabricate and assemble, but in which a new supply of line on a spool can be conveniently replaced without having to disassemble the portion of the unit including the biasing spring, and without having to significantly compress the spring during assembly. The arrangement of components also permit cam surfaces which are located relatively remote from the axis of the head, and thus have maximum leverages which results in minimum forces tending to wear and destroy the device.